1. Field of the Invention
The present invention relates generally to devices and methods for testing the durability of various materials, and more specifically to a machine and method for testing paving. The machine applies a rolling pressure to one or more pavement samples (e. g., asphalt) held in a tray within the machine. A hot water bath is also applied to the sample(s) in order to accelerate the effects of moisture and humidity thereon.
2. Description of the Related Art
The paving of roads, highways, parking areas, etc., has become an important part of our transportation system throughout the nation. Asphalt is by far the most commonly used paving medium used, with other materials (concrete, etc.) also being used. Initially, asphalt was made by mixing virtually any grade of tar or similar weight and viscosity petroleum product with sand, gravel, etc. This is still the basic method of forming asphalt paving material, but much has been learned about the quality of different ingredients therein and the proportions of materials which are used in the formation of asphalt paving.
Asphalt paving made from inferior ingredients, or in improper proportions, will not hold up as well as more carefully formed asphalt mixes. Also, different conditions require different mixes for optimum durability. Accordingly, various means have been developed in the past for testing asphalt and other paving materials. Most of these testing means utilize some form of test equipment installed on a road vehicle of some sort, with the vehicle then being driven over the subject paving area for testing. This has at least a few disadvantages in comparison to testing samples in a controlled environment in the laboratory. First, a relatively large expanse of pavement must be applied in order to provide a sufficient area over which a motor vehicle may be driven. Second, the environment of the test cannot be controlled when the paving is applied in an outdoor environment, as the environment is subject to heat, cold, rain, snow, etc. Third, in all likelihood such paving is subject to other traffic in addition to the test vehicle, with the other traffic comprising numerous vehicles of widely varying weights and speeds. Controlled testing in such conditions, and achieving consistent results, is all but impossible.
Accordingly, a need will be seen for a paving test machine and method capable of testing various samples of asphalt or other paving under tightly controlled conditions of temperature and humidity in an indoor laboratory environment. The machine accepts one or more paving samples and applies a repeated rolling pressure to the samples for a predetermined period of time or number of cycles, or until breakdown occurs. The machine provides precise measurements of the wear of the paving during testing, and automatically shuts off any one sample test if excessive wear occurs before all testing is complete. The machine is operated by computer control, and results are provided by the computer for later evaluation. A hot water bath may also be applied to the sample(s) in order to accelerate the effects of temperature and humidity on the sample(s).
A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is provided below.
U.S. Pat. No. 3,431,776 issued on Mar. 11, 1969 to George W. Hughes, titled "Road Surface Testing Device," describes a fifth wheel device applied to a motor vehicle and riding against the underlying surface. The fifth wheel is equipped with a brake, with the brake being applied when the vehicle is decelerating. The amount of braking pressure required before lockup of the wheel occurs, provides a measure of the surface friction of the underlying paving or other material. The Hughes device may be useful in testing the friction coefficient on airport runways and the like, but provides no information whatsoever relating to the durability or wear resistance of the paving, nor can the device provide a consistent test of a relatively small sample, as can the present invention.
U.S. Pat. No. 3,459,038 issued on Aug. 5, 1969 to Gilbert Swift, titled "Apparatus For Testing Road Surfaces And Method," describes a means for testing the roughness of a road surface. The means includes a fifth wheel secured to a motor vehicle, and a system for measuring the vertical motion of the wheel per unit of horizontal travel over a surface. The Swift apparatus and method do not provide for repetitive motion over a surface to measure the wear of that surface, nor does the Swift apparatus and method provide for the testing of a small sample in a controlled environment, as provided by the present invention.
U.S. Pat. No. 3,854,328 issued on Dec. 17, 1974 to Robert J. Schmidt, titled "Resiliency Testing Device," describes a fixture in which a sample may be placed for testing. The device applies a periodic compression to the subject material, with the material being rotated 90 degrees after a predetermined number of cycles for further testing. While the test sample may be placed in water, as in the present invention, the Schmidt device only applies a direct compressive load, with no rolling lateral load being applied to increase the pressure relatively gradually across the sample to simulate wear more accurately due to vehicle tires. Moreover, the Schmidt device is only capable of testing a single sample at a time, and Schmidt does not provide any means for automatically terminating the test when a predetermined wear or compression limit of the sample is reached, as provided in the present invention.
U.S. Pat. No. 3,888,118 issued on Jun. 10, 1975 to Jerry R. Nims, titled "Method And Apparatus For Determining Road Roughness," describes a device installed in a motor vehicle for testing the roughness of a surface over which the vehicle is driven. The device comprises a transducer and recorder installed in some spring suspended portion of the vehicle, and a cable connected. to an unsprung portion of the vehicle. As the vehicle is driven over a surface, any irregularities will result in the unsprung and spring suspended portions of the vehicle moving relative to one another, with the cable actuating the transducer to produce a recording of the degree of roughness. No means of measuring pavement wear is disclosed by Nims, nor is any means of measuring the wear of a sample in closely controlled conditions disclosed, as provided by the present invention.
U.S. Pat. No. 4,788,859 issued on Dec. 6, 1988 to Anwar S. Khattak, titled "Method And Apparatus For Determining Deflection In Pavement," describes an optical device placed in a vehicle and driven across the paved area subject to measurement. Obviously, no wear can be applied to the paved area by an optical testing means, which merely measures existing roughness or unevenness, rather than applying a weight to produce wear to a sample, as in the present invention. Also, the Khattak device and method cannot be applied to a relatively small sample in a machine in a controlled laboratory environment, as provided by the present invention.
U.S. Pat. No. 4,938,055 issued on Jul. 3, 1990 to Isami Tsuda, titled "Apparatus For Testing Abrasion," describes a device having a rotary turntable upon which paving samples are placed, with a grinding wheel, e. g., studded tire, rotating about a fixed axis. The rotation of the wheel causes the turntable to rotate, thereby periodically rotating the sample(s) beneath the wheel. Tsuda also provides a series of temperature control chambers opposite the wheel, through which the sample(s) is/are passed periodically. The present invention is constructed essentially opposite the Tsuda device, with the paving sample(s) being fixed in one or more trays, and the wheel(s) reciprocating linearly back and forth across the sample(s). Also, it is noted that Tsuda cannot provide continuous environmental conditions (heat, cold, etc.) for his samples, as they only periodically pass through the stationary environmental areas, and are clear of those areas when in contact with the abrasive wheel. The present invention provides continuous application of water at a predetermined temperature in order to apply such environmental influences continually during the test.
U.S. Pat. No. 5,365,793 issued on Nov. 22, 1994 to Ronald L. Terrel et al., titled "Equipment And Method For Environmental Testing Of Bituminous Specimens," describes a test cell in which a single sample core is placed, with a load cell providing periodic pneumatic compressive force to the sample. The test cell may be provided with water to alter the test environment. The Terrel et al. device does not apply a linear, reciprocating rolling force to the sample, as in the present invention.
Swiss Patent Publication No. 568,559 published on Oct. 31, 1975 to Jean-Claude Gressin illustrates a framework which may be secured beneath a vehicle (e. g., a truck) for measuring the roughness or unevenness of the underlying pavement or surface. The device is not applicable for use in a laboratory environment under controlled conditions, nor does the device produce and measure wear in a sample by providing a continuous reciprocating and rolling force to the sample, as in the case of the present invention.
British Patent Publication No. 2,067,769 published on Jul. 30, 1981 to Bergougnan-Benelux, titled "Measuring Static And Dynamic Material Characteristics," describes a device for imparting compressive force to a resilient material, e. g., rubber or the like. A relatively small spherical impression body is oscillated against the test sample over a relatively short distance. No means of rolling a movable test roller horizontally over the surface of a test article is disclosed in the British Patent Publication, nor is any means provided for adjusting moisture or humidity in the environment of the sample, as provided by the present invention.
Finally, Soviet Patent Publication No. 1,377,321 published on Feb. 29, 1988 illustrates a mechanical strain gauge linkage. The linkage is not suitable for imparting a force to a test sample, but only for measuring a deflection. No means for imparting a rolling force, nor for altering the moisture content of the sample environment, is evident in the Soviet Patent Publication.
None of the above inventions and patents, either singly or in combination, is seen to describe the instant invention as claimed.